Amelogenins are the major proteins expressed in the secretory enamel matrix, and appear to be important in regulating crystal growth in the mineralizing enamel matrix. The overall objective of this proposal is to study amelogenin expression in the developing rat incisor. Use of the rat incisor as a model system will allow us to compare expression of amelogenin at the various stages of enamel formation. The specific hypothesis to be tested is that at the secretory stage a number of amelogenin mRNA transcripts, some larger than 1kb are expressed, and at the maturation stage, expression is selective for smaller mRNA of less than 1.0 kb. The specific aims are : 1) to amplify , by PCR, the alternative 5' and 3' ends of amelogenin transcripts expressed during the secretory and the maturation stages of enamel formation. 2) to clone and sequence cDNAs amplified in specific aim l, and to compare these sequences to known amelogenin genomic and cDNA sequences. Rat enamel organ cDNA will be prepared from carefully isolated mRNA. Primers known' to hybridize with the major amelogenin transcripts of human and mouse will be used with anchored PCR to amplify the 5' and 3' ends of the amelogenin transcripts. The amplified ends of the amelogenin transcript will be cloned and sequenced. The cloned PCR products will be compared with the human genomic sequence to determine whether some of the amplified ends represent unspliced or partially spliced mRNA. Sequences obtained at the secretory stage will be compared to those obtained at the maturation stage of enamel formation, and the relationship between the sequences at the 2 stages will be determined. These studies of amelogenin mRNA will improve our knowledge of amelogenin expression in the developing enamel matrix. Studies of amelogenin protein-expression, will lead to a better understanding of the mechanisms involved in enamel formation, and perhaps broaden our knowledge of these proteins which are important in biomineralization. Understanding of these processes will enable us to determine which mechanisms may be altered in enamel pathologies and to ensure the formation of sound enamel.